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Re: procmail and mail file locking

2020-05-16 16:00:07

What Ruud posted is certainly good stuff but I got the impression from Robert's postings that this is overkill.

On Thu, 14 May 2020, at 22:26, Robert Moskowitz wrote:

Does procmail default lock the local delivery mail file as I have been told postfix and other MTAs do?

In case of files, yes.

If I run `procmail -f $MAILTO` where procmail is getting the mail file from STDIN.

That's fine. It does not change the default locking.

Or do I add something like the following to my script:

exec 100>/var/spool/mail$USER.lock || exit 1
flock -w 120 100 || exit 1

Not needed.

And do I also need -d $MAILTO on the above procmail call?

Not as long as $MAILTO is your own address.

On Fri, 15 May 2020, at 09:31, Robert Moskowitz wrote:

Se also https://linux.die.net/man/5/procmailrc
which mentions using lock files.

I am piping the output of a formail command into procmail.  No receipts.

Piping formail also doesn't change the fact that procmail has its default locking when delivering to files. But I did not get your remark about receipts.

It was that man page that clued me into needing to do something about locking the access to /var/spool/mail/$USER file.

It should work in most cases. Of course there are pathological cases like spool dirs mounted on network file systems or uncommon mail delivery agents (not that I know any).

But what is the 'common' lock file name?  The examples in the above mask the file which is the lock file.

/var/spool/mail/$USER.lock but see the manpages for details or run an strace if you want to be sure. I am actually not sure procmail creates a $LOCKEXT (defaults to .lock) file but I also did not bother to check. In any case quoting from procmail(1)

   Whenever procmail itself opens a file to deliver to, it
   consistently uses the following kernel locking strategies:
   fcntl(2).


--
-- Andreas


   Nothing in life is to be feared, it is only to be understood.
   Now is the time to understand more, so that we may fear less.

                  --- Glenn T. Seaborg, 1968, quoting Marie Curie; cf.
        https://todayinsci.com/C/Curie_Marie/CurieMarie-Quotations.htm
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